1. Field of the Invention
A spark-ignition engine has individual self-adaptive adjustment of the size of its fuel rations to individual cylinders, in dependence on misfires in those cylinders.
2. Description of the Prior Art
It has been found that the specific fuel consumption of a spark-ignition engine can be reduced by burning a lean fuel-air mixture. If the mixture is too lean, however, the engine will misfire on some of its combustion cycles. Excessive misfiring will increase the specific fuel consumption and the atmospheric emission of unburned hydrocarbons. Thus it is important for both fuel economy and low atmospheric pollution that the fuel-to-air ratio be maintained within a rather narrow range.
Adaptive methods for adjusting the overall fuel-to-air ratio were described in 1975 by Gorille et al. in paper no. 750368 of the Society of Automotive Engineers, and by Spilski and Creps, paper no. 750371 of the Society of Automotive Engineers. These methods use feedback from an exhaust gas sensor to keep the overall fuel-to-air ratio close to stoichimetric.
In multicylinder gasoline engines, the circumstances of combustion are often substantially different in different cylinders. When several cylinders receive a mixture of air and fuel from the same carburetor, some of the fuel may proceed as a liquid along the walls of the intake manifold in such a way as to enter the different cylinders in different amounts. The unequal distribution of fuel wastes somes of the fuel, causes atmospheric pollution, and may cause carbon deposits, fouling of the spark plugs, excessive misfiring, preignition, and engine knock.
One method for distributing fuel and air equally to all cylinders uses a separate carburetor for each cylinder. In each carburetor, a fuel reservoir at atmospheric pressure supplies fuel to the air stream through a metering orifice, the pressure drop across the metering orifice being produced by the rush of the air stream through a Venturi tube.
Other methods for distributing fuel equally to all cylinders employ continuous or timed fuel injection, in which the pressure in a common reservoir of fuel is kept well above atmospheric pressure. A separate fuel metering orifice is used for each cylinder, the fuel entering the air stream immediately in front of the air intake valve for that cylinder. In the case of timed fuel injection, an on-off valve is associated with each metering orifice, the size of the fuel ration for each cylinder being varied by changing the length of time that its valve is open during each cylinder cycle.
All of these methods of distributing fuel to the cylinders require metering orifices whose flow characteristics are constant in time. However, during the life of the engine, the metering orifices for the different cylinders may become fouled so that their flow characteristics change, seriously affecting the engine's specific fuel consumption and atmospheric emission. It is then necessary to test and adjust or to replace the metering orifices. Maintenance of a set of metering orifices which are identical within very close tolerances can add materialially to the cost of upkeep of the engine.
Apparatus which allows individual adjustment of the fuel rations to the different cylinders has been disclosed by Anderson in U.S. Pat. No. 3,835,819. Apparatus for diagnosing faults in individual cylinders has been disclosed by Bouverie in U.S. Pat. No. 4,179,922.